1. Field of the Invention
The present invention relates to a method for implementing MAC (Media Access Control) for an EPON (Ethernet Passive Optical Network) system defined in the IEEE (Institute of Electrical and Electronics Engineers) 802.3ah EFM (Ethernet in the First Mile) standard using general MAC based on an IEEE 802.3 standard.
2. Description of the Related Art
A PON (Passive Optical Network) system connects one OLT (Optical Line Termination) to a plurality of ONUs (Optical Network Units) using a 1×N ODN (Optical Distribution Network) to form a tree-type distribution topology.
The current IEEE 802.3ah EFM working group defined various functions necessary for an EPON (Ethernet Passive Optical Network) system. The three functions associated with MAC (Media Access Control) include an MPCP (Multi-Point Control Protocol) function, an OAM (Operation, Administration and Maintenance) function and an LLID (Logical Link ID) function. An LLID is positioned within a frame's preamble.
Referring to FIG. 1, layers based on a currently standardized and defined layering baseline are classified into a physical layer 102, data link layers 104 and an interface layer 106. The physical layer includes a PMA (Physical Medium Attachment) layer 108, a PMD (Physical Medium Dependent) layer 110 and a PCS (Physical Coding Sublayer) 112. Each data link layer 104 includes a MAC layer 114, an MPCP layer 116, a MAC control layer 118 and an OAM layer 120, a MAC client 122 residing above the OAM layer. Here, the higher client 122 can be a router, a switch, a ULSLE (Upper Layer Shared LAN Emulation) processor, etc. The interface layer 106 arranged between the physical layer 102 and the data link layers 104 includes the RS 124 which is an 802.3 MAC-PLS (Physical Layer Signaling) interface layer and a GMII (Gbps Media Independent Interface) layer 126.
In actual implementation, however, the plurality of MAC layers 114 shown is implemented as a single physical MAC layer. Through logical MAC emulation, the MAC functions for the EPON are carried out by the single physical MAC layer 114.
The MPCP and OAM functions each must be implemented in a layer higher than a MAC layer 114. An LLID tagging/detagging function must be implemented by an RS (Reconciliation Sublayer) 124.
Here, LLID information of a preamble must be available in other higher layers so that the emulation can be performed as if the single physical MAC layer 114 corresponds to the plurality of logical MAC layers. For example, an error counter must be managed on the basis of each LLID, and a packet must be generated and processed according to the LLID.
In other words, when PON (Passive Optical Network) layers are actually implemented, the single physical MAC layer 114, the MPCP layer 116 and the OAM layer 120 are used, and contents associated with the layers are separated according to the LLID. Accordingly, when an interface function is performed according to a higher MAC client 122 and the LLID, the emulation function can be appropriately performed.
FIG. 2 shows an exemplary format of an Ethernet frame based on the EFM standard. The frame includes an 8-byte preamble field 21, a 6-byte DA (Destination Address) field 22, a 6-byte SA (Source Address) field 23, a 2-byte L/T (Length/Type) field 24, a data/PAD (Packet Assembly and Disassembly) field 25 indicating frame data, and an FCS (Frame Check Sequence) field 26 which is arranged at the end of the frame and used for checking an error when information divided on a frame-by-frame basis is sent in data communication. The preamble field 21 includes a 3-byte SPD field 211, a 2-byte reserved field 212, a 2-byte LLID field 213 and a 1-byte CRC (Cyclical Redundancy Check) field 214.
FIG. 3 shows the conventional architecture for transferring a PON tagging Ethernet frame between layers, as disclosed in an application entitled “ETHERNET PASSIVE OPTICAL NETWORK SYSTEM (SAMSUNG ELECTRONICS CO., LTD.)”, filed in the Korean Industrial Property Office and assigned Serial No. 2002-35470.
In detail, the MAC layer 114 performs a basic operation for a frame transferred from the physical layer 102, and then a DA field 302, an SA field 304, an L/T field 306, a vLink tag field 308 and a data field 310 contained in the frame are transferred up to the MAC control layer 118 which first confirms the L/T field. Where a corresponding frame is a user frame, the L/T field 306 indicates a length value of the frame. In the case of the user frame, the MAC control layer 118 performs no operation, and transfers the DA field 302, the SA field 304 and the data field 310 to a higher layer.
At this time, the vLink tag field 308 is transferred as the user data field. The multiplexing layer 316 combines MAC addresses within the DA and SA fields 302, 304 and mode 312 and PHY_ID 314 data within the vLink tag field 308, and performs an appropriate reflection or forwarding operation according to a result of the combination. At this time, as the vLink tag field 308 follows the L/T field 306, the multiplexing layer 316 regards the vLink tag field 308 as general user data. The multiplexing layer transfers the vLink tag field 308 to a higher layer.
Further, a PHY_ID value 314 within the vLink tag field 308 varies with each mode. Where the mode is a P2P (Point-To-Point) mode, a PHY_ID value 314 of the destination is assigned. On the other hand, where the mode is an SCB (Single Copy Broadcasting) mode, a PHY_ID value 314 of an ONU transmitting a frame to a corresponding OLT is assigned. This assignment method is equally applicable to a downstream transmission.
The LLID information is contained in the preamble 21 of the Ethernet frame according to the current EFM standard shown in FIG. 2 and the preamble containing the LLID information 213 is transferred to a lower layer. In transferring the Ethernet frame to a higher layer, the preamble is removed. Problematically, the LLID information is therefore unavailable to the higher layer, and consequently a single MAC layer cannot be emulated.